The present invention relates to a power system including a power transfer device that prevents a common load from at once being powered by a main and auxiliary power source, and eliminates any possibility of back feeding the main power source from the auxiliary power source.
Reliance on electrical power in homes and industry causes power outages resulting from breakdowns in electrical utility equipment to become aggravating and oftentimes costly to varying degrees. The frequency of disruptions in utility electrical service has resulted in the popularity of standby generating equipment to supply at least critical load circuits. To accommodate these alternative electrical sources supplying common electrical load circuits, a power transfer switch is usually used. Such a transfer switch is normally conditioned to connect the utility source to the common load circuits, while maintaining generating equipment disconnected on standby. Upon the occurrence of a power outage, the transfer switch is thrown, either automatically or manually, to first disconnect the utility or main source and then connect the standby source or generator to the common load circuits. Obviously, precaution must be taken to ensure that the two sources can never be simultaneously connected to the common load circuits. In addition, where an auxiliary power source feeds an existing load center normally powered by a utility, the possibility of back feeding the utility with a generator through a common or neutral return conductor from the utility may exist, posing a safety hazard to utility workers dispatched to repair damaged power lines. Thus, there is a need for a power system that includes a power transfer device that prevents a common load from simultaneously being powered by a main and auxiliary power source, and eliminates any possibility of back feeding the main power source from the auxiliary power source.